Reflection optical device and imaging apparatus comprising it, multi-wavelength imaging apparatus, and vehicle mounted monitor

ABSTRACT

Reflection surfaces ( 2, 3 ) and a diaphragm ( 1 ) for limiting light fluxes disposed between an object and the reflection surface ( 2 ) that is located closest to the object are provided. At least one surface of the plural reflection surfaces ( 2, 3 ) has an anamorphic shape. The reflection surfaces ( 2, 3 ) are disposed eccentrically. There is provided a light shielding member ( 6 ) for blocking light fluxes passing through the diaphragm ( 1 ) and reaches the range to be imaged on an image surface ( 4 ) without being reflected by the reflection surfaces ( 2, 3 ). Since the shielding member ( 6 ) is disposed, unnecessary light fluxes do not reach the image surface directly. Since there is no refractive transmission plane, also unnecessary light reflected by the transmission plane does not reach the image surface.

TECHNICAL FIELD

[0001] The present invention relates to an optical system and an imagepickup device in each of which a reflection surface is used, andparticularly to an image pickup device using infrared rays.

BACKGROUND ART

[0002] Recently, research has been carried out on reflection opticaldevices mainly for the purpose of detection and image pickup of infraredrays. In particular, for instance, JP 63(1988)-503097A, JP1(1989)-502461A, JP 6(1994)-273671A, etc. propose various opticaldevices in which reflection surfaces are disposed eccentrically so thatlight fluxes are not blocked by the reflection surfaces on their way butare imaged effectively.

[0003] Furthermore, reflection optical devices in which a reflectionsurface is formed to be a free-form surface, though not for use withinfrared rays, is proposed by JP 8(1996)-292371A, for instance. However,in any devices, specifications such as brightness, resolution,distortion, an angle of view, etc. do not reach the practical level. Inorder to satisfy the practical level of specifications, we have proposeda reflection optical system formed of plural free-form surface mirrorsto date (International Publication Number WO 00/48033).

[0004] In a conventional optical system using not a reflection opticalsystem but instead a transmission surface, unnecessary light, which isreleased from a place other than an object and passes through adiaphragm, does not directly reach a pickup range in the image surface.However, there has been a problem in that a ghost image is generated,that is, unnecessary light reflected by the transmission surface reachesthe image surface. Furthermore, in the case where an extremely brightlight source (for example, sun, etc.) other than a pictured object ispresent near the object to be picked up, a ghost image commonly isgenerated. Such a ghost image can be prevented from being generated byforming an antireflection film, etc. on the transmission surface, but itis expensive and the cost rises.

[0005] However, the conventional reflection optical system as mentionedabove has a problem in that unnecessary light released from a placeother than an object passes through a diaphragm and reaches the pickuprange of the image surface without being reflected by the reflectionsurface. This problem is a new problem, that is, such a problem does notoccur in a lens system using a conventional transmission surface or areflection optical system that is not practical for the purpose of imagepickup. Therefore, in the reflection optical system, any techniques forpreventing such an unnecessary light from reaching the image surfacehave not been proposed particularly.

DISCLOSURE OF INVENTION

[0006] It is an object of the present invention to solve theabove-mentioned problems and to provide a reflection optical devicehaving a light shielding member in the reflection optical system,thereby improving the optical performance, realizing brightness and awide angle of view, and capable of preventing a ghost image from beinggenerated, an image pick up device using the same, a multiwavelengthimage pickup device and a vehicle-mounted monitoring device at low cost.

[0007] In order to achieve the above-mentioned object, a firstreflection optical device of the present invention includes pluralreflection surfaces and a diaphragm for limiting light fluxes, which isdisposed between an object and a reflection surface that is locatedclosest to the object among the plural reflection surfaces. At least oneof the plural reflection surfaces has an anamorphic shape, and theplural reflection surfaces are disposed eccentrically and form lightfluxes released from an object having a size not a spot into an image onan image surface. The reflection optical device comprises a lightshielding member for blocking light fluxes released from a place otherthan the object, which pass through the diaphragm and reach a pickuprange on the image surface without being reflected by the pluralreflection surfaces.

[0008] With such a reflection optical device, since the optical systemis formed of the reflection surfaces without using a transmissionsurface and the reflection surfaces are disposed eccentrically,effective light fluxes can be guided to the image surface without beingblocked. Furthermore, since the light shielding member is provided,unnecessary light fluxes do not directly reach the image surface. Inaddition, since there is not a refractive transmission surface,unnecessary light reflected by the transmission surface also does notreach the image surface. Therefore, a ghost image easily can beprevented from being generated.

[0009] In the above-mentioned reflection optical device, it ispreferable that the light shielding member is disposed between theobject and the diaphragm. With such a reflection optical device, sinceunnecessary light fluxes reliably can be blocked before entering theinside of the reflection optical system, a ghost image easily can beprevented from being generated.

[0010] Furthermore, it is preferable that the light shielding member isa plate-shaped member having one end located at the side of thediaphragm and the other end extending to the object. With such areflection optical device, it is possible to provide a light shieldingmember at low cost.

[0011] Furthermore, it is preferable that the light shielding member hasan inclined surface for limiting light fluxes released from the objectin the direction in which the light fluxes travel from the side of theobject to the side of the diaphragm so that effective light fluxes,which form an image on the image surface, are not blocked.

[0012] Furthermore, it is preferable that the light shielding member isintegrated with the diaphragm. With such a reflection optical device, aprocess of disposing the light shielding member in the diaphragm part isomitted, thus simplifying the manufacture and reducing the cost.

[0013] Furthermore, it is preferable that the plural reflection surfacesand the image surface are disposed inside the housing; the diaphragm isan aperture provided in the housing; and the light shielding member isdisposed outside the housing. With such a reflection optical device,unnecessary light fluxes are blocked before entering the housing, andtherefore unnecessary light fluxes reliably can be prevented fromentering the optical system.

[0014] Furthermore, it is preferable that the number of the pluralreflection surfaces is two; the shape of the two reflection surfaces isanamorphic; and when the two reflection surfaces are referred to as afirst reflection surface and a second reflection surface in that orderfrom the side of the object, the light shielding member is disposed in aspace surrounded by an optical axis extending from the vertex of thefirst reflection surface to the vertex of the second reflection surface,an optical axis extending from the vertex of the second reflectionsurface to the center of the image surface, and a line connecting thecenter of the image surface and the vertex of the first reflectionsurface in a plane including the center of the image surface and thevertices of the two reflection surfaces. With such a reflection opticaldevice, a space for blocking unnecessary light fluxes without blockingeffective light fluxes is found in the optical system and the lightshielding member is disposed in this space. Therefore, it is possible toprevent a ghost image from being generated while miniaturizing thedevice, thus enabling an excellent image pickup.

[0015] Furthermore, it is preferable that the number of the pluralreflection surfaces is four; and when the four reflection surfaces arereferred to as a first reflection surface, a second reflection surface,a third reflection surface and a fourth reflection surface in that orderfrom the side of the object, the light shielding member is disposed in aspace surrounded by an optical axis extending from the vertex of thesecond reflection surface to the vertex of the third reflection surface,an optical axis extending from the vertex of the third reflectionsurface to the vertex of the fourth reflection surface, and a lineconnecting the vertex of the second reflection surface and the vertex ofthe fourth reflection surface in a plane including the center of theimage surface and the vertices of the four reflection surfaces. Withsuch a reflection optical device, a space for blocking unnecessary lightfluxes without blocking effective light fluxes is found in the opticalsystem and the light shielding member is disposed in this space.Therefore, it is possible to prevent a ghost image from being generatedwhile miniaturizing the device, thus enabling an excellent image pickup.

[0016] Furthermore, it is preferable that the outer shape of the lightshielding member is adjusted so as not to block the effective lightfluxes that form an image on the image surface.

[0017] Furthermore, it is preferable that the following relationship issatisfied:

3≦Wy≦30

[0018] where Wy (deg) denotes a half angle of view in the Y direction ina plane including vertices of the reflection surface in the rectangularcoordinate system (X, Y) in which the X direction is a directionperpendicular to a plane including the center of the image surface andthe vertices of the reflection surfaces and the Y direction is atangential direction of the plane including vertices of the reflectionsurface at the vertex included in this plane. When the angle of view islarger than the upper limit of this conditional relationship, it becomesdifficult to correct aberration. On the other hand, when it is smallerthan the lower limit, it is difficult to use the device as an imagepickup device.

[0019] Furthermore, it is preferable that the following relationship issatisfied

0.95≦Fno.≦3.1

[0020] where Fno. denotes an open F value in a plane including thevertices of the four reflection surfaces. When the brightness is higherthan the upper limit of this conditional relationship, it becomesdifficult to achieve MTF of 20% or more at 20 (l.p/mm) due to theinfluence of the refraction in the case where the far-infrared regionwith wavelength of 10 μm is picked up. On the other hand, when thebrightness is lower than the lower limit it is difficult to correctaberration.

[0021] Furthermore, it is preferable that the number of the pluralreflection surfaces is four and the following relationships aresatisfied:

0.95≦Fno.≦3.1

3≦Wy<10

[0022] where Fno. denotes an open F value in a plane including thevertices of the four reflection surfaces, and Wy (deg) denotes a halfangle of view in the Y direction in a plane including the vertices ofthe reflection surfaces in the rectangular coordinate system (X, Y) inwhich the X direction is a direction perpendicular to a plane includingthe center of the image surface and the vertices of the reflectionsurfaces and the Y direction is a tangential direction at a vertexincluded in this plane. With such a reflection optical device, it ispossible to realize an extremely bright reflection optical devicealthough the angle of view is narrow. Furthermore, the effect ofblocking unnecessary light by the light shielding member is added, andthereby excellent telescopic image pickup can be realized. In therelationship of Fno., when the value is larger than the upper limit, itbecomes difficult to improve the resolution due to the influence of therefraction in the case of picking up an image in the far-infrared regionand when it is smaller than the lower limit it becomes difficult tocorrect aberration.

[0023] Furthermore, it is preferable that the number of the pluralreflection surfaces is four and the following relationships aresatisfied:

1.1≦Fno.≦3.1

10≦Wy<20

[0024] where Fno. denotes an open F value in a plane including thevertices of the four reflection surfaces, and Wy (deg) denotes a halfangle of view in the Y direction in a plane including the vertices ofthe reflection surfaces in the rectangular coordinate system (X, Y) inwhich the X direction is a direction perpendicular to a plane includingthe center of the image surface and the vertices of the reflectionsurfaces and the Y direction is a tangential direction at a vertexincluded in this plane. With such a reflection optical device, it ispossible to realize a reflection optical device that is extremely brightalthough the angle of view is narrow. Furthermore, the effect ofblocking unnecessary light by the light shielding member is added, andthereby a slightly telescopic image pickup having general versatilitycan be realized. In the relationship of Fno., when the value is largerthan the upper limit, it becomes difficult to improve the resolution dueto the influence of the refraction in the case of picking up an image inthe far-infrared region and when it is smaller than the lower limit itbecomes difficult to correct aberration.

[0025] Furthermore, it is preferable that the number of the pluralreflection surfaces is four and the following relationships aresatisfied:

1.4≦Fno.≦3.1

20≦Wy<30

[0026] where Fno. denotes an open F value in a plane including thevertices of the four reflection surfaces, and Wy (deg) denotes a halfangle of view in the Y direction in a plane including the vertices ofthe reflection surfaces in the rectangular coordinate system (X, Y) inwhich the X direction is a direction perpendicular to a plane includingthe center of the image surface and the vertices of the reflectionsurfaces and the Y direction is a tangential direction at a vertexincluded in this plane. With such a reflection optical device, it ispossible to realize a reflection optical device that is extremely brightalthough the angle of view is narrow. Furthermore, the effect ofblocking unnecessary light by the light shielding member is added, andthereby a slightly telescopic image pickup having general versatilitycan be realized. In the relationship of Fno., when the value is largerthan the upper limit, it becomes difficult to improve the resolution dueto the influence of the refraction in the case of picking up an image inthe far-infrared region and when it is smaller than the lower limit, itbecomes difficult to correct aberration.

[0027] Furthermore, in the above-mentioned reflection optical devices inwhich Fno. is limited, it is preferable that the relationship: Fno.≦1.9is satisfied. With such a reflection optical device, for example, evenif there is an influence of the refraction when the far-infrared regionwith wavelength of 10 μm is picked up, it is possible to achieve MTF of20% or more at 35 (l.p/mm).

[0028] Furthermore, in the above-mentioned reflection optical devices inwhich Fno. is limited, it is preferable that the relationship: Fno.≦1.6is satisfied. With such a reflection optical device, for example, it ispossible to achieve MTF of 20% or more at 40 (l.p/mm).

[0029] Furthermore, it is preferable that the shape of at least onesurface of the plural reflection surfaces is a free-form surface thatdoes not have a rotational central axis. By using the free-form surface,more practical optical performance can be obtained.

[0030] Next, the image pickup device of the present invention includesthe above-mentioned reflection optical device and a detector forconverting light intensity into an electrical signal. According to suchan image pickup device, since the reflection optical device of thepresent invention is used, it is possible to realize an image pickupdevice that prevents a ghost image from being generated while improvingthe optical performance.

[0031] In the above-mentioned image pickup device, it is preferable thatthe detector is a two-dimensional image pickup element. With such animage pickup device, it is possible to obtain a picture image having awide angle of view and high resolution.

[0032] Furthermore, it is preferable that the detector has sensitivitywith respect to light beams in the infrared region.

[0033] Next, a first multiwavelength image pickup device of the presentinvention includes the above-mentioned reflection optical device and adetector having sensitivity with respect to light beams in pluraldifferent wavelength bands. According to the above-mentionedmultiwavelength image pickup device, since the reflection optical deviceof the present invention is used, it is possible to obtain amultiwavelength image pickup device that prevents a ghost image frombeing generated while improving the optical performance. Furthermore,since the optical system is formed only of reflection surfaces, it canbe used in any of regions from the infrared region (wavelength: 3-5 μmor 8-12 μm) to the visible region (wavelength: 400-750 nm), and theultraviolet region (wavelength: 200-400 nm). Furthermore, by combiningthe optical system with a detector having sensitivity in pluralwavelength regions, it is possible to pick up picture images in pluralwavelength bands with one optical system simultaneously. For example, ifthe detector has sensitivity with respect to light beams of bothinfrared region and visible region, the visible region suitable forimage pickup in the daytime and infrared region suitable for imagepickup at night become possible.

[0034] In the first multiwavelength image pickup device, it ispreferable that the detector has a light flux dividing member fordividing light fluxes into light fluxes in different wavelength bandsand detection surfaces corresponding to the plural divided wavelengthbands. With such a multiwavelength image pickup device, it is possibleto pick up images in plural wavelength bands by one optical systemsimultaneously. For example, if the detector has sensitivity withrespect to light beams of both infrared region and visible region, thevisible region suitable for image pickup in the daytime and infraredregion suitable for image pickup at night become possible.

[0035] Next, a second multiwavelength image pickup device includes theabove-mentioned reflection optical device and the detector having pluralregions, which have sensitivity with respect to light beams in differentwavelength bands, in the same detecting plane. According to theabove-mentioned multiwavelength image pickup device, it is possible topick up plural images with one optical system and one detection elementsimultaneously.

[0036] Next, a first vehicle-mounted monitoring device of the presentinvention includes the above-mentioned image pickup device and a displayfor conveying a picked-up picture image to a driver. According to theabove-mentioned vehicle-mounted monitoring device, since a display isprovided in addition to the image pickup device of the presentinvention, it is possible to obtain location information such asvehicles going in front, people, etc. with high precision.

[0037] Next, a second vehicle-mounted monitoring device of the presentinvention includes the above-mentioned multiwavelength image pickupdevice and a display for conveying a picked-up picture image to adriver. According to the above-mentioned vehicle-mounted monitoringdevice, since a display is provided in addition to the image pickupdevice of the present invention, it is possible to obtain locationinformation such as vehicles going in front, people, etc. with highprecision.

BRIEF DESCRIPTION OF DRAWINGS

[0038]FIG. 1 is a view showing a configuration of a reflection opticaldevice according to a first embodiment of the present invention.

[0039]FIG. 2 is a perspective view to explain the shape of a reflectionsurface.

[0040]FIG. 3 is an aberration view showing an optical performance of areflection optical device according to Example 1.

[0041]FIG. 4 is an aberration view showing an optical performance of areflection optical device according to Example 2.

[0042]FIG. 5 is a view showing a configuration of a reflection opticaldevice according to a second embodiment of the present invention.

[0043]FIG. 6 is a view showing a configuration of a reflection opticaldevice according to a third embodiment of the present invention.

[0044]FIG. 7 is an aberration view showing an optical performance of areflection optical device according to Example 3.

[0045]FIG. 8 is an aberration view showing an optical performance of areflection optical device according to Example 4.

[0046]FIG. 9 is an aberration view showing an optical performance of areflection optical device according to Example 5.

[0047]FIG. 10 is an aberration view showing an optical performance of areflection optical device according to Example 6.

[0048]FIG. 11 is a view showing a configuration of a reflection opticaldevice according to a fourth embodiment of the present invention.

[0049]FIG. 12 is a view showing a configuration of a pickup deviceaccording to a fifth embodiment of the present invention.

[0050]FIG. 13 is a view showing a configuration of a multiwavelengthimage pickup device according to a sixth embodiment of the presentinvention.

[0051]FIG. 14 is a view showing a configuration of a multiwavelengthimage pickup device according to a seventh embodiment of the presentinvention.

[0052]FIG. 15 is a view showing a configuration of a vehicle-mountedmonitoring device according to an eighth embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0053] Hereinafter, the present invention will be explained by way of anembodiment with reference to the accompanying drawings.

[0054] (First Embodiment)

[0055]FIG. 1 is a view showing a configuration of a reflection opticaldevice according to the first embodiment of the present invention. InFIG. 1, reference numeral 1 denotes a diaphragm, 2 denotes a firstmirror, 3 denotes a second mirror, 4 denotes an image surface, 5 denotesa housing and 6 denotes a light shielding plate. Light fluxes releasedfrom the object travel in the direction shown by an arrow A, are limitedby the diaphragm 1 and incident in the housing 5. These incident lightfluxes are reflected by the first mirror 2 and the second mirror 3,which are disposed obliquely with respect to the optical axis, that is,disposed eccentrically, and form an image on the image surface 4. Inother words, in the reflection optical device of this embodiment, asshown in FIG. 1, light fluxes released from an object having a size nota spot are imaged to form an image having a size on the image surface 4(the same is true in the following embodiments).

[0056] In order to block outside light from a place other than the imagepickup range a, an optical system including the first mirror 2 and thesecond mirror 3 and the image surface 4 are surrounded by the housing 5.In this embodiment, the light shielding plate 6 that is a means forblocking light is further provided. The light shielding plate 6 isdisposed in front of the diaphragm 1 (at the side of the object withrespect to the diaphragm 1) with one end located at the side of thediaphragm 1 and the other end extending to the side of the object.Furthermore, in order not to shield effective light fluxes released fromthe object and forming an image on the image surface 4, an inclined face6 a disposed so that the light fluxes released from the object arelimited as traveling from the side of the object to the diaphragm 1.Also in the embodiments shown with reference to FIGS. 6 and 12 to 14,such a light shielding plate is disposed. Furthermore, also in theembodiments with reference to each figure, the light shielding plates 15and 21 have inclined planes 15 a and 21 a, respectively.

[0057] Herein, a region b shows an unnecessary light flux transmissionregion. In the case where the light shielding member 6 is not provided,unnecessary light fluxes entering from the diaphragm 1 pass through theunnecessary light flux transmission region b and directly reach theimage surface 4. In this embodiment, since the light shielding plate 6is disposed in front of the diaphragm 1, the unnecessary light fluxesare shielded before entering the housing 5. Thus, the unnecessary lightfluxes are prevented from entering the inside of the optical systemreliably.

[0058] That is, the light shielding plate 6 is disposed so as to blockthe unnecessary light fluxes released from a place other than the objectand reaching the image pickup region on the image surface 4 withoutbeing reflected by the first mirror 2 and the second mirror 3.

[0059] The surface shape of the first mirror 2 and the second mirror 3is an anamorphic surface, in which the normal line at the vertex is nota rotationally symmetric axis unlike a general spherical surface and anaxially symmetric non-spherical surface. If the reflection surface ofthe anamorphic surface is assumed to be a free-form surface, the degreeof freedom of design increases, so that the angle can be made wider andthe optical performance can be improved.

[0060] The free-form surface herein denotes a surface without having arotational central axis possessed by a toric surface, etc. (the same istrue in the following embodiments). An example of the free-form surfaceincludes a curved-axis Y toric surface as shown in FIG. 2. Thecurved-axis Y toric surface is a surface in which a line connecting thecenters of the radius of curvature of the cross section in the Xdirection of each Y coordinate is a curved line in the rectangularcoordinate system (X, Y) in which the X direction is a directionperpendicular to a plane including the center of the image surface andthe vertices of the reflection surfaces and the Y direction is atangential direction at a vertex included in this plane. In FIG. 2, L1denotes a cross-sectional shape (arc) in the X direction, L2 denotes aline connecting the centers of the radius of curvatures of thecross-sectional shape (not an arc-shaped curved line) in the Xdirection, L3 denotes a shape (not arc) of the surface in the Ydirection and P denotes a vertex. Furthermore, there may be an X toricsurface in which X and Y are replaced by each other.

[0061] With the premise that the vertex of the plane is the origin andthe direction in which an incident light flux travels forward ispositive, the curved-axis Y toric surface is expressed as a sag amount Z(mm) from the vertex at a point with the coordinates x (mm) and y (mm),which is expressed by Formulae (1) through (5). $\begin{matrix}{{Z = {{M(y)} + {S\left( {x,y} \right)}}}{{M(y)} = {\frac{\left( \frac{y^{2}}{Rdy} \right)}{1 + \sqrt{1 - \left( \frac{y}{Rdy} \right)^{2}}} + {{YAD}\quad y^{4}} + {{YAE}\quad y^{6}} + {{YAF}\quad y^{8}} + {{YAG}\quad y^{10}} + {{YAOD}\quad y^{3}} + {{YAOE}\quad y^{5}} + {{YAOF}\quad y^{7}} + {{YAOG}\quad y^{9}}}}} & {{Formula}\quad (1)} \\{{S\left( {x,y} \right)} = {\frac{\frac{x^{2}}{Rds} - {2{x \cdot \sin}\quad \theta}}{{\cos \quad \theta} + \sqrt{{\cos^{2}\theta} - \left( \frac{x}{Rds} \right)^{2} + \frac{2{x \cdot \sin}\quad \theta}{Rds}}} + {{XAD}\quad x^{4}} + {{XAE}\quad x^{6}} + {{XAF}\quad x^{8}} + {{XAG}\quad x^{10}}}} & {{Formula}\quad (2)}\end{matrix}$

Rds=Rdx(1+BCy ² +BDy ⁴ +BEy ⁶ +BFy ⁸ +BGy ¹⁰ +BOCy+BODy ³ +BOEy ⁵ +BOFy⁷ +BOGy ⁹)  Formula (4)

θ=QCy ² +QDy ⁴ +QEy ⁶  Formula (5)

[0062] In the above-mentioned formulae, M(y) denotes an expression thatexpresses a non-arc as Y direction cross-sectional shape including thevertex. Rdy (mm) denotes a radius of curvature in the Y direction, andYAD, YAE, YAF and YAG denote even-order constants contributing in the Ydirection respectively and YAOD, YAOE, YAOF, and YAOG denote odd-orderconstants, respectively. S(x, y) denotes an expression that expresses anX direction cross-sectional shape. Rds denotes a function that expressesa radius of curvature in the X direction at each Y coordinate; Rdx (mm)denotes a radius of curvature in the X direction at the center; BC, BD,BE, BF and BG denote even-order constants, respectively; BOC, BOD, BOE,BOF and BOG denote odd-order constants, respectively; XAD, XAE, XAF andXAG denote even-order constants contributing in the X direction; θ (rad)is a function that determines a twist angle; and QC, QD and QE denotetwist coefficients, respectively.

[0063] With the premise that the vertex of the plane is the origin andthe direction in which an incident light flux travels forward ispositive, the curved-axis X toric surface is expressed as a sag Z (mm)from the vertex at a point with the coordinates x (mm) and y (mm), whichis expressed by Formulae (6) through (10).

Z=M(x)+S(x, y)  Formula (6) $\begin{matrix}{{{M(x)} = {\frac{\left( \frac{x^{2}}{Rdx} \right)}{1 + \sqrt{1 - \left( \frac{x}{Rdx} \right)^{2}}} + {{XAD}\quad x^{4}} + {{XAE}\quad x^{6}} + {{XAF}\quad x^{8}} + {{XAG}\quad x^{10}}}}\quad} & {{{Formula}\quad (7)}\quad} \\\begin{matrix}{{S\left( {x,y} \right)} = {\frac{\frac{y^{2}}{Rds} - {2{y \cdot \sin}\quad \theta}}{{\cos \quad \theta} + \sqrt{{\cos^{2}\theta} - \left( \frac{y}{Rds} \right)^{2} + \frac{2{y \cdot \sin}\quad \theta}{Rds}}} +}} \\{{{{YAD}\quad y^{4}} + {{YAE}\quad y^{6}} + {{YAF}\quad y^{8}} + {{YAG}\quad y^{10}} +}} \\{{{{YAOD}\quad y^{3}} + {{YAOE}\quad y^{5}} + {{YAOF}\quad y^{7}} + {{YAOG}\quad y^{9}}}}\end{matrix} & {{Formula}\quad (8)}\end{matrix}$

Rds=Rdy(1+BCx ² +BDx ⁴ +BEx ⁶ +BFx ⁸ +BGx ¹⁰ +BOCx+BODx ³ +BOEx ⁵ +BOFx⁷ +BOGx ⁹)  Formula (9)

θ=QCx ² +QDx ⁴ +QEx ⁶  Formula (10)

[0064] In the above-mentioned formulae, M(x) denotes an expression thatexpresses a non-arc as an X-direction cross-sectional shape includingthe vertex, S (x, y) denotes an expression that expresses a Y directioncross-sectional shape. Rdx (mm) denotes a radius of curvature in the Xdirection, XAD, XAE, XAF and XAG denote even-order constantscontributing in the X-direction, respectively; and Rds denotes afunction that expresses a radius of curvature in the Y direction at eachx-coordinate, Rdy (mm) denotes a radius of curvature in the Y directionat the center; BC, BD, BE, BF and BG denote even-order constants,respectively; BOC, BOD, BOE, BOF and BOG denote odd-order constants,respectively; YAD, YAE, YAF and YAG denote even-order constants,respectively; YAOD, YAOE, YAOF and YAOG denote odd-order constants,respectively; θ (rad) denotes a function that determines a twist angleof the surface; and QC, QD and QE denote twist coefficients,respectively.

[0065] Furthermore, when the half angle of view (deg) in the Y directionin the plane including vertices of the reflection surface is Wy, Wypreferably satisfies the following Formula (11). When the angle of viewis larger than the value expressed by Formula (11), it is difficult tocorrect aberration. When the angle is smaller than the lower limit, itbecomes difficult to use the device as a pickup device.

3≦Wy≦30  Formula (11)

[0066] Next, Table 1 and Table 2 show specific examples of a number ofthe embodiments. In each table, M1 denotes the first mirror 2 and M2denotes the second mirror 3. In Example 1 of Table 1, both M1 and M2 arecurved-axis Y toric surfaces and in Example 2 of Table 2, both M1 and M2are curved-axis X toric surfaces, and the shape of the diaphragm iscircular in both embodiments.

[0067] Furthermore, Wy denotes a half angle of view (deg) in the Ydirection in the plane including vertices of the reflection surface, Wxdenotes a half angle of view (deg) in the X direction in the planeincluding vertices of the reflection surface, efy denotes a focal length(mm) of the entire system in the Y direction, efx denotes a focal length(mm) of the entire system in the X direction, Fny denotes an F value inthe Y direction, Fnx denotes an F value in the X direction, d1 denotes adistance (mm) from the center of the diaphragm 1 to the vertex of thefirst mirror 2, d2 denotes a distance (mm) from the vertex of the firstmirror 2 to the vertex of the second mirror 3, d3 denotes a distance(mm) from the vertex of the second mirror 3 to the center of the imagesurface 4, α1 denotes an angle (deg) made by a normal line of the firstmirror 2 and an optical axis, α2 denotes an angle (deg) made by a normalline of the second mirror 3 and an optical axis, and α3 denotes an angle(deg) made by a normal line of an image surface 4 and the optical axis.TABLE 1 efy = 8.59 efx = 29.58 Wy = 20 Wx = 10 Fny = 4.30 Fnx = 14.79Diaphragm Circular: Φ2.0 d1: 6.61  M1 α1: 30 (Curved-axis rdy: −15.07698rdx: −161.387 Y toric surfaces) YAD: 1.4254 × 10⁻⁵ YAOD: −7.5192 × 10⁻⁴YAOE: 1.6213 × 10⁻⁵ BC: 9.2330 × 10⁻³ BOD: 3.4719 × 10⁻³ d2: 23.41 M2α2: 30 (Curved-axis rdy: −22.108 rdx: −56.202 Y toric surfaces) YAD:−2.2097 × 10⁻⁵ YAOD: 3.3323 × 10⁻⁴ YAOE: 2.7018 × 10⁻⁷ BC: −1.7039 ×10⁻³ BOD: 7.7878 × 10⁻⁵ d3: 22.16 Image surface α3: 0 

[0068] TABLE 2 efy = 9.75 efx = 24.94 Wy = 10 Wx = 5 Fny = 3.25 Fnx =8.31 Diaphragm Circular: Φ3.0 d1: 8.15  M1 α1: 30 (Curved-axis rdy:−15.40531 rdx: −78.23718 X toric YAD: −1.11104 × 10⁻⁶ YAE: −7.94940 ×10⁻⁶ surfaces) YAF: 3.20283 × 10⁻⁷ YAG: 5.58089 × 10⁻¹⁰ YAOD: 1.28434 ×10⁻³ YAOE: 1.02160 × 10⁻⁵ YAOF: −3.52620 × 10⁻⁷ YAOG: 1.28002 × 10⁻⁸XAD: 2.97163 × 10⁻⁵ XAE: 2.42403 × 10⁻⁶ BC: −4.08445 × 10⁻⁴ BD: −1.37960× 10⁻⁴ QC: 1.45193 × 10⁻⁴ QD: −2.89601 × 10⁻⁶ d2: 17.89 M2 α2: 30(Curved-axis rdy: 14.82636 rdx: 58.27511 X toric YAD: 1.41004 × 10⁻⁵YAE: −8.10057 × 10⁻⁷ surfaces) YAF: −1.08431 × 10⁻⁸ YAG: 3.22948 × 10⁻⁹YAOD: 2.08556 × 10⁻⁴ YAOE: −3.49859 × 10⁻⁶ YAOF: 9.93788 × 10⁻⁸ YAOG:3.43238 × 10⁻⁹ XAD: −9.91702 × 10⁻⁷ XAE: 1.65342 × 10⁻⁶ BC: −8.01946 ×10⁻⁴ BD: 3.67792 × 10⁻⁵ QC: 3.07422 × 10⁻⁴ QD: 1.64131 × 10⁻⁶ d3: 15.02Image surface   α3: 23.74

[0069]FIG. 3 is aberration views showing an optical performance of thereflection optical device according to Example 1 of Table 1, and FIG. 4is aberration views showing an optical performance of the reflectionoptical device according to Example 2 of Table 2.

[0070] According to this embodiment, since two curved toric surfacemirrors having a function of correcting aberration with high precisionare disposed eccentrically, effective light fluxes can be guided to theimage surface without being blocked and image can be formed on the imagesurface efficiently. Furthermore, since a light shielding plate 6 isdisposed, unnecessary light fluxes do not reach the image surfacedirectly. In addition, since no refractive transmission surfaces areprovided, unnecessary light reflected by the transmission surface doesnot reach the image surface. Therefore, it is easy to prevent a ghostimage from being generated.

[0071] Furthermore, Wy=20 is realized in Example 1 of Table 1, and Wy=10is realized in the second Example 2 of Table 2, and Formula (11) issatisfied.

[0072] Note here that the embodiment shown in FIG. 1 explains an examplein which the diaphragm 1 and the external light shielding plate 6, whichare formed individually, are bonded. However, these may be formed intoone piece. Thus, since the process for securing the external lightshielding plate 6 onto the part of the diaphragm 1 can be omitted, it ispossible to facilitate the manufacture and to reduce the cost.

[0073] Furthermore, in this embodiment, the shape of the mirror surfacewas defined by Formulae 1 through 5 or Formulae 6 through 10. However,the shape is not necessarily limited to this and it may be another shapedefined by a different formula as long as the similar surface can berealized.

[0074] (Second Embodiment)

[0075]FIG. 5 is a view showing a configuration of a reflection opticaldevice according to the second embodiment of the present invention. Thebasic configuration of the embodiment shown in FIG. 5 is the same asthat of the first embodiment shown in FIG. 1 excepting the arrangementof the light shielding plate 7 that is a means for blocking light. Thesame numbers are given to the portions having the same configurations.

[0076] In this embodiment, the light shielding plate 7 is disposedinside the housing 5. Specifically, the light shielding plate 7 isdisposed in a space surrounded by an optical axis extending from thevertex of the first reflection surface 2 to the vertex of the secondreflection surface 3, an optical axis extending from the vertex of thesecond reflection surface 3 to the center of the image surface 4, and aline connecting between the center of the image surface 4 and the vertexof the first reflection surface 2 in a plane including the center of theimage surface 4 and the vertex of the reflection surface 2, 3.

[0077] That is, the light shielding plate 7 is disposed so that itblocks unnecessary light fluxes reaching the pickup range on the imagesurface 4 without being reflected by the reflection surfaces of thefirst mirror 2 and the second mirror 3. Thus, unnecessary light fluxesare blocked reliably before reaching the pickup range on the imagesurface 4. In this embodiment, since the light shielding plate 7 isdisposed inside the housing 5, it is advantageous that the device can bemade smaller in this embodiment as compared with the embodiment 1.

[0078] Note here that it is not necessary for the entire light shieldingplate 7 to be disposed inside the above-mentioned space, but a parthaving a role of blocking light in the light shielding plate 7, that is,only a light shielding surface, may be disposed in the above-mentionedspace. Furthermore, the outer shape of the light shielding plate 7 isadjusted so as not to block effective light fluxes that form an image onthe image surface 4.

[0079] (Third Embodiment)

[0080]FIG. 6 is a view showing a configuration of a reflection opticaldevice according to the third embodiment of the present invention. InFIG. 6, reference numeral 8 denotes a diaphragm, 9 denotes a firstmirror, 10 denotes a second mirror, 11 denotes a third mirror, 12denotes a fourth mirror, 13 denotes an image surface, 14 denotes ahousing, and 15 denotes a light shielding plate. Light fluxes releasedfrom the object are limited at the diaphragm 8 and incident in thehousing 14. These incident light fluxes are reflected by the firstmirror 9, the second mirror 10, the third mirror 11 and the fourthmirror 12 and form an image on the image surface 13. The first, secondand third mirrors 9 through 11 are disposed obliquely with respect tothe optical axis, that is, disposed eccentrically so that the lightfluxes are reflected obliquely.

[0081] In order to block the outside light from a place other than theimage pickup range c, an optical system including the first mirror 9,the second mirror 10, the third mirror 11 and the forth mirror 12 andthe image surface 13 are surrounded by the housing 14. In thisembodiment, a light shielding plate 15 that is a means for blockinglight is further provided. The light shielding plate 15 is disposed infront of the diaphragm 8 (at the side of the object with respect to thediaphragm 1) with one end located at the side of the diaphragm 8 and theother end extending to the side of the object. Furthermore, an inclinedsurface 15 a is disposed so as not to block the light fluxes releasedfrom the object.

[0082] Herein, a region d shows an unnecessary light flux transmissionregion. In the case where the light shielding plate 15 is not provided,unnecessary light fluxes entering from the diaphragm 8 pass through theunnecessary light flux transmission region d and directly reach theimage surface 13. In this embodiment, since the light shielding plate 15is disposed in front of the diaphragm 8, the unnecessary light fluxesare shielded before entering the housing 14. Thus, the unnecessary lightfluxes are prevented from entering the inside of the optical systemreliably.

[0083] That is, the light shielding plate 15 is disposed so as to blockthe unnecessary light fluxes released from a place other than the objectand reaching the image pickup region on the image surface 13 withoutbeing reflected by the first mirror 9, the second mirror 10, the thirdmirror 11 and the fourth mirror 12.

[0084] For the surface shape of the first mirror 9, the second mirror10, the third mirror 11 and fourth mirror 12, a curved-axis Y-toricsurface (see FIG. 2) or a curved-axis X-toric surface are used, whichare defined by Formulae (1) through (5) or Formulae (6) through (10).

[0085] Furthermore, when an open F value in the plane including verticesof the four reflection surfaces is expressed by Fno., Fno. preferablysatisfies the following relationship formula (12). It is because whenthe brightness is higher than the upper limit of Formula (12), forexample, under the influence of the diffraction in the case where thefar-infrared region with wavelength of 10 μm is picked up, it becomesdifficult to achieve MTF of 20% or more at 20 (l.p/mm), and when thebrightness is lower than the lower limit, it is difficult to correct theaberration.

0.95≦Fno.≦3.1  Formula (12)

[0086] Furthermore, it is preferable that the following formulae (13)and (14) are satisfied. Thus, it is possible to provide a reflectionoptical device that is extremely bright although the angle of view isnarrow, and the effect of shielding unnecessary light by the lightshielding plate 15 is added, thereby realizing excellent telescopicimage pickup. In Formula (14), if the value is larger than the upperlimit, when the pickup in the far-infrared region is carried out, it isdifficult to improve the resolution due to the effect of diffraction,and when the value is lower than the lower limit, it is difficult tocorrect the aberration.

3≦Wy<10  Formula (13)

0.95≦Fno.≦3.1  Formula (14)

[0087] Furthermore, the device may satisfy the following Formulae (15)and (16). Thus, it is possible to provide a reflection optical devicethat is bright although the angle of view is narrow, and the effect ofshielding unnecessary light by the light shielding plate 15 is added,thereby realizing excellent image pickup that is rather telescopic andhas general versatility. In Formula (16), when the value is higher thanthe upper limit, it becomes difficult to improve the resolution due tothe influence of the diffraction in the case where the pickup in the farinfrared region is carried out, and when the value is lower than thelower limit, it is difficult to correct aberration.

10≦Wy<20  Formula (15)

1.1≦Fno.≦3.1  Formula (16)

[0088] Furthermore, the device may satisfy the following Formulae (17)and (18). Thus, it is possible to provide a reflection optical devicethat is bright although the angle of view is narrow, and the effect ofblocking unnecessary light by the light shielding plate 15 is added,thereby realizing an excellent image pickup that is rather wide-angleand has general versatility. In Formula (18), when the value is higherthan the upper limit, it becomes difficult to improve the resolution dueto the influence of the diffraction in the case where the pickup in thefar infrared region is carried out, and when the value is lower than thelower limit, it is difficult to correct aberration.

20≦Wy<30  Formula (17)

1.4≦Fno.≦3.1  Formula (18)

[0089] Furthermore, with respect to the above-mentioned formulae (12),(14), (16) or (18) showing the relationship of Fno., preferably, thefollowing formula (19) is satisfied, and more preferably, the followingformula (20) is satisfied.

Fno.≦1.9  Formula (19)

Fno.≦1.6  Formula (20)

[0090] When Formula (19) is satisfied, even under the influence of thediffraction in the case where pickup in the far-infrared region with awavelength of, for example, 10 μm is carried out, it is possible toachieve MTF of 20% or more at 35 (l.p/mm), and when Formula (20) issatisfied, it is possible to achieve MTF of 20% or more at 40 (l.p/mm).

[0091] Next, Tables 3 through 6 show the specific numerical examples ofthis embodiment. In each table, M1 denotes the first mirror 9, M2denotes the second mirror 10, M3 denotes the third mirror 11 and M4denotes the fourth mirror 12. In each Example of each table, M1 and M4are the curved-axis X toric surfaces and M2 and M3 are the curved-axis Ytoric surfaces. The shape of the diaphragm is a circle in Examples 3through 5 shown in Tables 3 through 5, and is an oval (diameter in the Ydirection=ely and diameter in the X direction elx) in Example 6 shown inTable 6.

[0092] Furthermore, Wy denotes a half angle of view (deg) in the Ydirection in a plane including vertices of the reflection surface; Wxdenotes a half angle of view (deg) in the Y direction in a planeincluding vertices on the reflection surface; efy denotes a focal length(mm) of the entire system in the Y direction; efx denotes a focal length(mm) of the entire system in the X direction; Fny denotes an F value inthe Y direction; Fnx denotes an F value in the X direction; d1 denotes adistance (mm) from the center of the diaphragm 8 to the vertex of thefirst mirror 9; d2 denotes a distance (mm) from the vertex of the firstmirror 9 to the vertex of the second mirror 10; d3 denotes a distance(mm) from the vertex of the second mirror 10 to the reflex of the thirdmirror 11; d4 denotes a distance (mm) from the vertex of the thirdmirror 11 to the vertex of the fourth mirror 12; and d5 denotes adistance (mm) from the vertex of the fourth mirror 12 to the center ofthe image surface 13.

[0093] Furthermore, α1 denotes an angle (deg) made by a normal line ofthe first mirror 9 and an optical axis; β2 denotes an angle (deg) madeby a normal line of the second mirror 10 and an optical axis; α3 denotesan angle (deg) made by a normal line of the third mirror 11 and anoptical axis; α4 denotes an angle (deg) made by a normal line of thefourth mirror 12 and an optical axis; and α5 denotes an angle (deg) madeby a normal line of the image surface 13 and an optical axis. TABLE 3efy = 4.95 efx = 8.2 Wy = 5 Wx = 5 Fny = 0.95 Fnx = 1.58 DiaphragmCircular: Φ5.2 d1: 3.70 M1 α1: 45 (Curved-axis rdy: −28.27521 rdx:−105.98079 X toric surfaces) YAD: 1.02556 × 10⁻⁴ YAE: 2.83097 × 10⁻⁶YAOD: 5.06972 × 10⁻⁴ YAOE: −3.75050 × 10⁻⁵ XAD: −1.0962 × 10⁻⁴ XAE:3.2316 × 10⁻⁶ BC: 1.29266 × 10⁻² BD: 6.31068 × 10⁻⁴ BE: −1.12113 × 10⁻⁴QC: −5.70442 × 10⁻⁴ QD: 2.94019 × 10⁻⁵ QE: −1.83285 × 10⁻⁶ d2: 9.6  M2α2: 45 (Curved-axis rdy: 41.39209 rdx: −27.71945 Y toric surfaces) YAD:−7.16742 × 10⁻⁵ YAE: −3.45971 × 10⁻⁸ YAOD: −1.52126 × 10⁻⁴ YAOE:−2.22863 × 10⁻⁶ BC: 7.78348 × 10⁻³ BD: 6.35020 × 10⁻⁴ BE: 1.39808 × 10⁻⁴BOC: −7.32163 × 10⁻² BOD: −2.44275 × 10⁻³ BOE: −3.23971 × 10⁻⁴  d3:22.17 M3   α3: 37.5 (Curved-axis rdy: −43.65138 rdx: −17.39224 Y toricsurfaces) YAD: 1.17856 × 10⁻⁶ YAE: 4.88859 × 10⁻⁸ YAOD: 5.53600 × 10⁻⁵YAOE: 4.28108 × 10⁻⁷ BC: −1.00083 × 10⁻³ BO: −4.03599 × 10⁻⁷ BE:−9.68610 × 10⁻⁹ BOC: −5.54207 × 10⁻³ BOD: 2.48896 × 10⁻⁵ BOE: −3.60009 ×10⁻⁷  d4: 22.57 M4 α4: 30 (Curved-axis rdy: 20.69789 rdx: 7.04215 Xtoric surfaces) YAD: 1.26072 × 10⁻⁴ YAE: −4.27173 × 10⁻⁶ YAF: 1.51652 ×10⁻⁷ YAG: −9.76524 × 10⁻¹⁰ YAOD: 2.61273 × 10⁻⁴ YAOE: 2.13618 × 10⁻⁵YAOF: −3.79231 × 10⁻⁷ YAOG: 1.03312 × 10⁻⁸ XAD: −7.44221 × 10⁻⁵ XAE:−5.76785 × 10⁻⁷ BC: −1.84455 × 10⁻² BD: −1.68089 × 10⁻⁵ BE: 1.09803 ×10⁻⁵ QC: −7.05260 × 10⁻⁴ QD: −7.44136 × 10⁻⁶ QE: 6.10570 × 10⁻⁷ d5: 7.7 Image surface α5: 16

[0094] TABLE 4 efy = 4.95 efx = 8.2 Wy = 10 Wx = 10 Fny = 1.10 Fnx =1.82 Diaphragm Circular: Φ4.5 d1: 3.70 M1 α1: 45 (Curved-axis rdy:−28.27225 rdx: −105.69323 X toric surfaces) YAD: 1.08844 × 10⁻⁴ YAE:3.06546 × 10⁻⁶ YAOD: 5.65907 × 10⁻⁴ YAOE: −4.12477 × 10⁻⁵ XAD: −1.31496× 10⁻⁴ XAE: 7.43903 × 10⁻⁷ BC: 1.01233 × 10⁻² BD: 6.01015 × 10⁻⁴ BE:−7.92244 × 10⁻⁵ QC: −4.25193 × 10⁻⁴ QD: 4.34592 × 10⁻⁵ QE: −1.01385 ×10⁻⁶ d2: 9.6  M2 α2: 45 (Curved-axis rdy: 39.64773 rdx: −27.72966 Ytoric surfaces) YAD: −5.60488 × 10⁻⁶ YAE: −2.34213 × 10⁻⁷ YAOD: −6.70024× 10⁻⁵ YAOE: −1.27702 × 10⁻⁶ BC: 7.48019 × 10⁻³ BD: 2.72224 × 10⁻⁴ BE:6.59806 × 10⁻⁷ BOC: −7.03043 × 10⁻² BOD: −1.70279 × 10⁻³ BOE: −1.65868 ×10⁻⁵  d3: 22.19 M3   α3: 37.5 (Curved-axis rdy: −43.64144 rdx: −17.39145Y toric surfaces) YAD: 8.44053 × 10⁻⁷ YAE: 5.20757 × 10⁻⁸ YAOD: 5.00413× 10⁻⁵ YAOE: 6.68626 × 10⁻⁷ BC: −9.95660 × 10⁻⁴ BD: −8.00549 × 10⁻⁷ BE:−6.10841 × 10⁻⁹ BOC: −5.62691 × 10⁻³ BOD: 4.06888 × 10⁻⁵ BOE: −1.35045 ×10⁻⁹  d4: 22.57 M4 α4: 30 (Curved-axis rdy: 20.69433 rdx: 7.04381 Xtoric surfaces) YAD: 1.29951 × 10⁻⁴ YAE: −4.20345 × 10⁻⁶ YAF: 1.51679 ×10⁻⁷ YAG: −1.02477 × 10⁻⁹ YAOD: 2.77413 × 10⁻⁴ YAOE: 2.06307 × 10⁻⁵YAOF: −3.87449 × 10⁻⁷ YAOG: 1.03479 × 10⁻⁸ XAD: −7.92485 × 10⁻⁵ XAE:−1.56111 × 10⁻⁶ BC: −1.94353 × 10⁻² BD: −8.36210 × 10⁻⁵ BE: 7.90330 ×10⁻⁶ QC: −6.60836 × 10⁻⁴ QD: −6.90683 × 10⁻⁶ QE: 3.15739 × 10⁻⁷ d5: 7.7 Image surface α5: 16

[0095] TABLE 5 efy = 4.95 efx = 8.2 Wy = 20 Wx = 10 Fny = 1.41 Fnx =2.34 Diaphragm Circular: Φ3.5 d1: 3.70 M1 α1: 45 (Curved-axis rdy:−28.36101 rdx: −106.68403 X toric surfaces) YAD: 1.10697 × 10⁻⁴ YAE:2.99391 × 10⁻⁶ YAOD: 5.79682 × 10⁻⁴ YAOE: −4.14654 × 10⁻⁵ XAD: −1.29369× 10⁻⁴ XAE: 3.35450 × 10⁻⁷ BC: 1.11679 × 10⁻² BD: 6.83405 × 10⁻⁴ BE:−7.47472 × 10⁻⁵ QC: −3.87840 × 10⁻⁴ QD: 3.81498 × 10⁻⁵ QE: −2.08261 ×10⁻⁶ d2: 9.6  M2 α2: 45 (Curved-axis rdy: 39.31311 rdx: −27.92454 Ytoric surfaces) YAD: −2.16018 × 10⁻⁷ YAE: −2.99374 × 10⁻⁸ YAOD: −5.60292× 10⁻⁵ YAOE: −7.09183 × 10⁻⁷ BC: 7.55866 × 10⁻³ BD: 2.71136 × 10⁻⁴ BE:2.69578 × 10⁻⁷ BOC: −7.07328 × 10⁻² BOD: −1.68621 × 10⁻³ BOE: −1.72513 ×10⁻⁵  d3: 22.15 M3   α3: 37.5 (Curved-axis rdy: −43.63003 rdx: −17.35842Y toric surfaces) YAD: 7.18754 × 10⁻⁷ YAE: 5.41462 × 10⁻⁸ YAOD: 4.82396× 10⁻⁵ YAOE: 6.70946 × 10⁻⁷ BC: −9.91360 × 10⁻⁴ BD: −7.75342 × 10⁻⁷ BE:−7.57007 × 10⁻⁹ BOC: −5.65695 × 10⁻³ BOD: 4.13483 × 10⁻⁵ BOE: 1.39452 ×10⁻⁸ d4: 22.5 M4 α4: 30 (Curved-axis rdy: 20.71904 rdx: 7.03109 X toricsurfaces) YAD: 1.30093 × 10⁻⁴ YAE: −4.17720 × 10⁻⁶ YAF: 1.52547 × 10⁻⁷YAG: −1.00136 × 10⁻⁹ YAOD: 2.74354 × 10⁻⁴ YAOE: 2.05378 × 10⁻⁵ YAOF:−3.86108 × 10⁻⁷ YAOG: 1.04814 × 10⁻⁸ XAD: −7.90990 × 10⁻⁵ XAE: −1.59051× 10⁻⁶ BC: −1.94677 × 10⁻² BD: −8.78028 × 10⁻⁵ BE: 7.74365 × 10⁻⁶ QC:−6.58999 × 10⁻⁴ QD: −7.68549 × 10⁻⁶ QE: 2.82293 × 10⁻⁷ d5: 7.7  Imagesurface α5: 16

[0096] TABLE 6 efy = 4.95 efx = 8.2 Wy = 25 Wx = 5 Fny = 2.91 Fnx = 2.73Diaphragm Oval: ely = 1.75 elx = 3.0 d1: 3.70 M1 α1: 45 (Curved-axisrdy: −27.84486 rdx: −96.60869 X toric surfaces) YAD: 1.03513 × 10⁻⁴ YAE:3.01919 × 10⁻⁶ YAOD: 7.51834 × 10⁻⁴ YAOE: −3.99463 × 10⁻⁵ XAD: 1.82513 ×10⁻⁵ XAE: −5.81005 × 10⁻⁶ BC: 2.73116 × 10⁻³ BD: 3.53144 × 10⁻³ BE:8.60275 × 10⁻⁵ QC: −6.41736 × 10⁻⁴ QD: 1.31645 × 10⁻⁴ QE: 1.20688 × 10⁻⁶d2: 9.6  M2 α2: 45 (Curved-axis rdy: 37.58249 rdx: −27.59662 Y toricsurfaces) YAD: −1.04090 × 10⁻⁶ YAE: −1.15960 × 10⁻⁷ YAOD: −5.89613 ×10⁻⁵ YAOE: 1.70106 × 10⁻⁷ BC: 7.59351 × 10⁻³ BD: 2.69631 × 10⁻⁴ BE:3.41035 × 10⁻⁷ BOC: −6.78696 × 10⁻² BOD: −1.69850 × 10⁻³ BOE: −1.65408 ×10⁻⁵  d3: 21.99 M3   α3: 37.5 (Curved-axis rdy: −43.41434 rdx: −17.43582Y toric surfaces) YAD: 7.25332 × 10⁻⁷ YAE: 4.58233 × 10⁻⁸ YAOD: 3.15841× 10⁻⁵ YAOE: 7.17088 × 10⁻⁷ BC: −9.77416 × 10⁻⁴ BD: −1.30884 × 10⁻⁶ BE:−4.46350 × 10⁻⁸ BOC: −5.51823 × 10⁻³ BOD: 3.97945 × 10⁻⁵ BOE: 9.75707 ×10⁻⁸  d4: 22.54 M4 α4: 30 (Curved-axis rdy: 20.65812 rdx: 7.02149 Xtoric surfaces) YAD: 1.19275 × 10⁻⁴ YAE: −4.27123 × 10⁻⁶ YAF: 1.63843 ×10⁻⁷ YAG: −3.47605 × 10⁻¹⁰ YAOD: 2.30792 × 10⁻⁴ YAOE: 1.96160 × 10⁻⁵YAOF: −3.53296 × 10⁻⁷ YAOG: 1.29639 × 10⁻⁸ XAD: −9.00698 × 10⁻⁵ XAE:−1.06708 × 10⁻⁶ BC: −2.05610 × 10⁻² BD: −1.83324 × 10⁻⁴ BE: −9.97323 ×10⁻⁶ QC: −7.81636 × 10⁻⁴ QD: −1.09010 × 10⁻⁵ QE: −1.17753 × 10⁻⁶ d5:7.7  Image surface α5: 16

[0097]FIGS. 7 through 10 are aberration views showing an opticalperformance of the reflection optical device according to Examples 3through 6 shown in Tables 3 through 6. Example 3 (Table 3) and Example 4(Table 4) show a telescopic image pickup system. As is apparent fromeach Table, an extremely bright F value is achieved. Example 5 shown inTable 5 (Table 5) satisfies an angle of view having general versatilityand brightness. As is apparent from FIG. 10, in Example 6 (Table 6), awide angle of view is realized. Furthermore, in Example 6, as shown inTable 6, the shape of the diaphragm is assumed to be an oval elongatedin the X direction and the F value in the X direction is made to bebright. Therefore, even under the influence of the diffraction,practical resolution can be obtained.

[0098] According to this embodiment, four mirrors having curved-axis Xtoric surface shape or curved-axis Y toric surface having a function ofcorrecting aberration with high precision are arranged eccentrically, itis possible to guide effective fluxes to the image surface without beingblocked and an optical image can be formed excellently.

[0099] Furthermore, since the light shielding plate 15 is disposed,unnecessary light fluxes cannot reach the image surface. In addition,since a refractive transmission surface is not provided, unnecessarylight reflected by the transmission surface also does not reach theimage surface. Therefore, it is easy to prevent a ghost image from beinggenerated.

[0100] Furthermore, in Example 3 shown in Table 3, the reflectionoptical device satisfying Wy=5, Fny=0.95 and Fnx=1.58 and theabove-mentioned formulae (13), (14) and (20) is realized. In Example 4shown in Table 4, the reflection optical device satisfying Wy=10,Fny=1.10 and Fnx=1.82 and the above-mentioned formulae (15), (16) and(19) is realized. In Example 5 shown in Table 5, the reflection opticaldevice satisfying Wy=20, Fny=1.41 and Fnx=2.34 and the above-mentionedformulae (17) and (18) is realized. In Example 6 shown in Table 6, thereflection optical device satisfying Wy=25, Fny=2.91 and Fnx=2.73 andthe above-mentioned formulae (17) and (18) is realized. Furthermore, anyof the Examples shown in Tables 3 through 6 satisfy the above-mentionedformula (11),

[0101] Furthermore, the shape of the mirror is not necessarily limitedto those expressed by Formulae (1) through (5) or Formulae (6) through(10), and may have any shapes expressed by different definition formulaeas long as the same shape is realized.

[0102] (Fourth Embodiment)

[0103]FIG. 11 is a view showing a configuration of the reflectionoptical device according to the fourth embodiment of the presentinvention. The basic configuration of the embodiment shown in FIG. 11 isthe same as that of the first embodiment shown in FIG. 6 excepting thearrangement of the light shielding plate 16 that is a means for blockinglight. The same numbers are given to the portions having the sameconfigurations.

[0104] In this embodiment, the light shielding plate 16 is disposedinside the housing 14. The light shielding plate 16 is disposed in aspace surrounded by an optical axis extending from the vertex of thereflection surface of the second mirror 10 to the vertex of thereflection surface of the third mirror 11, an optical axis extendingfrom the vertex of the reflection surface of the third mirror 11 to thevertex of the reflection surface of the fourth mirror 12; and the lineconnecting the vertex of the reflection surface of the second mirror 10and the vertex of the reflection surface of the fourth mirror 12 so thatthe unnecessary light does not reach the image surface 13.

[0105] That is, the light shielding plate 16 is disposed so as to blockunnecessary light fluxes released from a place other than the object andreaching the image pickup range on the image surface 13 without beingreflected by the reflection surfaces of the mirrors 9 through 12. Thus,the unnecessary light flux can be blocked reliably before reaching theimage pickup range on the image surface 13. In this embodiment, sincethe light shielding plate 16 is disposed in the housing 14, it isadvantageous that the device can be made smaller as compared with theembodiment 4.

[0106] Furthermore, explanations for the above-mentioned formulae (11)through (20) similarly can be applied to this embodiment.

[0107] (Fifth Embodiment)

[0108]FIG. 12 is a view showing a configuration of the reflectionoptical device according to the fifth embodiment of the presentinvention. The pickup device shown in FIG. 12 includes an opening window17, a first mirror 18, a second mirror 19, a housing 20, a lightshielding plate 21 and a two-dimensional image pickup element 22 that isan optical detector for converting light intensity into an electricalsignal. The arrangement of the first mirror 18 and the second mirror 19,and the plane shapes thereof are the same as those in the firstembodiment. The opening window 17 has a function as an aperture stopthat transmits the wavelength band necessary to image pickup and at thesame time limits the diameter of the light flux and also has a functionfor preventing dust particles from entering the optical system.

[0109] The light fluxes released from the object are limited at theopening window 17 disposed at the location of the diaphragm, and theimage is formed on the two-dimensionally image pickup element 22 by wayof the first mirror 18 and the second mirror 19. Also in thisembodiment, since a light shielding plate 21 that is a means forblocking light is provided, unnecessary light fluxes are blocked and anexcellent image can be obtained. In this embodiment, a picture imagethat is converted into the electrical signal at the two-dimensionallyimage pickup 22 is output (an arrow (e)).

[0110] According to this embodiment, the reflection optical system thatis the same as that in the first embodiment 1 and a detector forconverting light intensity into an electrical signal are provided andfurther the two dimensional image pickup element is used as thedetector. Therefore, it is possible to obtain a picture signal having awide angle of view and high resolution. Furthermore, if atwo-dimensional image pick element having sensitivity to light beams inthe infrared region (in the range of the wavelength from 3 to 5 μm or inthe range of the wavelength from 8 to 12 μm). is used, the infraredimage can be picked up.

[0111] (Sixth Embodiment)

[0112]FIG. 13 is a view showing a configuration of the multiwavelengthpickup device according to the sixth embodiment of the presentinvention. In FIG. 13, the configurations represented by referencenumerals 17 through 21 are the same as those in the Fifth Embodiment. Inthe Sixth Embodiment, a wavelength selection filter 23 that is a lightflux dividing means, an infrared image pickup element 24 that is adetector for converting the light intensity into the electrical signaland a visible image pickup element 25 are provided.

[0113] The wavelength selection filter 23 transmits only light beams inthe infrared range (in the range of the wavelength from 3 to 5 μm or inthe range of the wavelength from 8 to 12 μm) and reflects light beams inthe visible range (in the range of the wavelength from 400 to 750 μm).The infrared image pickup element 24 has sensitivity with respect tolight beams in the infrared region and the visible range image pickupelement 25 has the sensitivity with respect to light beams in thevisible region.

[0114] The light fluxes in two wavelength bands (visible region andinfrared region) released from the object are limited at the openingwindow 17 disposed at the location of the diaphragm, formed into aconverging flux by the mirror formed of two mirrors 18 and 19, and onlythe light fluxes in the infrared range pass through the wavelengthselection filter 23 and are imaged on the infrared image pick element 24and a picture image that is converted into an electrical signal isoutput (an arrow (f)).

[0115] On the other hand, the light fluxes in the visible regionreflected by the wavelength selection filter 23 form an image on thevisible image pickup element 25 and the picture image that is convertedinto an electrical signal is output (an arrow (g)).

[0116] According to this embodiment, since the reflection optical systemthat is the same as that in the first embodiment is used, unnecessarylight fluxes can be blocked by a light shielding plate 21 that is ameans for blocking light and excellent optical image can be obtained.Furthermore, since the light fluxes in the two wavelength bands form animage by the optical system formed of only mirrors in which no coloraberration occurs, for the wavelength bands of both visible region andthe infrared region, an excellent optical performance can be achieved.

[0117] (Seventh Embodiment)

[0118]FIG. 14 is a view showing a configuration of the multiwavelengthpickup device according to the seventh embodiment of the presentinvention. In FIG. 14, the configurations represented by referencenumerals 17 through 21 are the same as those in the Fifth Embodiment. Inthe Seventh Embodiment, a multiwavelength image pickup element 26 thatis a detector having the sensitivity with respect to the light beams forboth the infrared region and the visible light is provided. Themultiwavelength image pickup element 26 has plural regions havingsensitivity with respect to the light beams in the different wavelengthbands (infrared region and visible region) in the same detecting plane.

[0119] The light fluxes in the two wavelength bands (visible region andinfrared region) released from the object are limited at the openingwindow 17 disposed at the location of the diaphragm, and form an imageon the infrared image pick element 26 by the mirror formed of twomirrors 18 and 19. Also in this embodiment, since unnecessary lightfluxes are blocked by the light shielding plate 21 that is a means forblocking light, an excellent image can be obtained. Furthermore, sincethe light fluxes in the two wavelength bands form an image by theoptical system formed of only mirrors in which no color aberrationoccurs, for the wavelength bands of both visible region and the infraredregion, an excellent optical performance can be achieved.

[0120] Furthermore, in the multiwavelength image pickup element 26, aregion having sensitivity with respect to the visible region and theregion having sensitivity with respect to the infrared light region aredisposed in one image pickup plane discretely. Therefore, the pictureimages in the two wavelength bands are converted into two kinds ofelectrical signals in the far infrared picture signal (an arrow (h)) andthe visible region picture signal (an arrow (i)).

[0121] (Eighth Embodiment)

[0122]FIG. 15 is a view showing a configuration of a vehicle-mountedmonitoring device according to the eight embodiment of the presentinvention. The vehicle-mounted monitoring device shown in FIG. 15includes a, multiwavelength pickup device 27 and the display 28 that isa displaying means.

[0123] The picture image in the two wavelength bands (visible region andinfrared region) output from the multiwavelength pickup device 27 isdisplayed by the display device 28 and a driver can obtain informationas necessary. For example, in the case where the outside is bright inthe daytime, information can be obtained mainly from the picture imageby the visible light. In the nighttime, valuable information such as thelocation of people, vehicles, etc. can be obtained from the pictureimage by the infrared rays. That is, according to this embodiment, it ispossible to obtain the location information of oncoming cars, people,etc. regardless of day and night with high precision.

[0124] Note here that the multiwavelength pickup device using the pickupdevice of the fifth embodiment and the multiwavelength pickup device ofthe sixth and seventh embodiments was explained as an example that isthe same as in the first embodiment, however, reflection optical systemsthat are the same as in the second through fourth embodiments may beused.

[0125] Furthermore, the multiwavelength pickup device using thevehicle-mounted monitoring device of the eight embodiment was explainedas the example of the multiwavelength pickup device that is the same asin the seventh embodiment, however, the reflection optical systems thatare the same as in the second to fought embodiments may be used.

INDUSTRIAL APPLICABILITY

[0126] As mentioned above, according to the reflection optical device ofthe present invention, the optical system is formed of the reflectionsurface without using a transmission surface and the reflection surfacesare disposed eccentrically. Therefore, the effective light fluxes can beguided to the image surface without being blocked. Furthermore, since alight shielding member is provided, unnecessary light fluxes do notdirectly reach the image surface. In addition, a refractive transmissionsurface is not provided, the unnecessary light reflected by thetransmission does not reach the image surface. Therefore, it is possibleto prevent a ghost image from being prevented easily, the device can beused for the pickup device, multiwavelength pickup device or avehicle-mounted monitoring device.

1. A reflection optical device comprising: plural reflection surfaces,and a diaphragm for limiting light fluxes, which is disposed between anobject and a reflection surface that is located closest to the objectamong the plural reflection surfaces, wherein at least one of the pluralreflection surfaces has an anamorphic shape, and the plural reflectionsurfaces are disposed eccentrically and light fluxes released from anobject having a size not a spot are imaged to form an image having asize on an image surface, and, the reflection optical device comprises alight shielding member for blocking light fluxes released from a placeother than the object, which pass through the diaphragm and reach apickup range on the image surface without being reflected by the pluralreflection surfaces.
 2. The reflection optical device according to claim1, wherein the light shielding member is disposed between the object andthe diaphragm.
 3. The reflection optical device according to claim 2,wherein the light shielding member is a plate-shaped member having oneend located at the side of the diaphragm and the other end extendingtoward the object.
 4. The reflection optical device according to claim3, wherein the light shielding member has an inclined surface forlimiting light fluxes released from the object in the direction in whichthe light fluxes travel from the side of the object to the side of thediaphragm so that effective light fluxes, which form an image on theimage surface, are not blocked.
 5. The reflection optical deviceaccording to claim 2, wherein the light shielding member is integratedwith the diaphragm.
 6. The reflection optical device according to claim1, wherein the plural reflection surfaces and the image surface aredisposed inside the housing; the diaphragm is an aperture provided inthe housing; and the light shielding member is disposed outside thehousing.
 7. The reflection optical device according to claim 1, whereinthe number of the plural reflection surfaces is two; the shape of thetwo reflection surfaces is anamorphic; and when the two reflectionsurfaces are referred to as a first reflection surface and a secondreflection surface in that order from the side of the object, the lightshielding member is disposed in a space surrounded by an optical axisextending from the vertex of the first reflection surface to the vertexof the second reflection surface, an optical axis extending from thevertex of the second reflection surface to the center of the imagesurface, and a line connecting the center of the image surface and thevertex of the first reflection surface in a plane including the centerof the image surface and the vertices of the two reflection surfaces. 8.The reflection optical device according to claim 7, wherein the outershape of the light shielding member is adjusted so as not to blockeffective light fluxes that form an image on the image surface.
 9. Thereflection optical device according to claim 1, wherein the number ofthe plural reflection surfaces is four; and when the four reflectionsurfaces are referred to as a first reflection surface, a secondreflection surface, a third reflection surface and a fourth reflectionsurface in that order from the side of the object, the light shieldingmember is disposed in a space surrounded by an optical axis extendingfrom the vertex of the second reflection surface to the vertex of thethird reflection surface, an optical axis extending from the vertex ofthe third reflection surface to the vertex of the fourth reflectionsurface, and a line connecting the vertex of the second reflectionsurface and the vertex of the fourth reflection surface in a planeincluding the center of the image surface and the vertices of the fourreflection surfaces.
 10. The reflection optical device according toclaim 9, wherein the outer shape of the light shielding member isadjusted so as not to block the effective light fluxes that form animage on the image surface.
 11. The reflection optical device accordingto claim 1, wherein the following relationship is satisfied: 3≦Wy≦30where Wy (deg) denotes a half angle of view in the Y direction in aplane including vertices of the reflection surface in the rectangularcoordinate system (X, Y) in which the X direction is a directionperpendicular to a plane including the center of the image surface andthe vertices of the reflection surfaces and the Y direction is atangential direction of the plane including vertices of the reflectionsurface at the vertex included in this plane.
 12. The reflection opticaldevice according to claim 9, wherein the following relationship issatisfied: 0.95≦Fno.≦3.1 where Fno. denotes an open F value in a planeincluding the vertices of the four reflection surfaces.
 13. Thereflection optical device according to claim 12, wherein the followingrelationship is satisfied: Fno.≦1.9.
 14. The reflection optical deviceaccording to claim 12, wherein the following relationship is satisfied:Fno.≦1.6.
 15. The reflection optical device according to claim 1,wherein the number of the plural reflection surfaces is four and thefollowing relationships are satisfied: 0.95≦Fno.≦3.1 3≦Wy<10 where Fno.denotes an open F value in a plane including the vertices of the fourreflection surfaces, and Wy (deg) denotes a half angle of view in the Ydirection in a plane including the vertices of the reflection surfacesin the rectangular coordinate system (X, Y) in which the X direction isa direction perpendicular to a plane including the center of the imagesurface and the vertices of the reflection surfaces and the Y directionis a tangential direction at a vertex included in this plane.
 16. Thereflection optical device according to claim 15, wherein the followingrelationship is satisfied: Fno.≦1.9.
 17. The reflection optical deviceaccording to claim 15, wherein the following relationship is satisfied:Fno.≦1.6.
 18. The reflection optical device according to claim 1,wherein the number of the plural reflection surfaces is four and thefollowing relationships are satisfied: 1.1≦Fno.≦3.1 10≦Wy<20 where Fno.denotes an open F value in a plane including the vertices of the fourreflection surfaces, and Wy (deg) denotes a half angle of view in the Ydirection in a plane including the vertices of the reflection surfacesin the rectangular coordinate system (X, Y) in which the X direction isa direction perpendicular to a plane including the center of the imagesurface and the vertices of the reflection surfaces and the Y directionis a tangential direction at a vertex included in this plane.
 19. Thereflection optical device according to claim 18, wherein the followingrelationship is satisfied: Fno.≦1.9.
 20. The reflection optical deviceaccording to claim 18, wherein the following relationship is satisfied:Fno.≦1.6.
 21. The reflection optical device according to claim 1,wherein the number of the plural reflection surfaces is four and thefollowing relationships are satisfied: 1.4≦Fno.≦3.1 20≦Wy<30 where Fno.denotes an open F value in a plane including the vertices of the fourreflection surfaces, and Wy (deg) denotes a half angle of view in the Ydirection in a plane including the vertices of the reflection surfacesin the rectangular coordinate system (X, Y) in which the X direction isa direction perpendicular to a plane including the center of the imagesurface and the vertices of the reflection surfaces and the Y directionis a tangential direction at a vertex included in this plane.
 22. Thereflection optical device according to claim 21, wherein the followingrelationship is satisfied: Fno.≦1.9.
 23. The reflection optical deviceaccording to claim 21, wherein the following relationship is satisfied:Fno.≦1.6.
 24. The reflection optical device according to claim 1,wherein the shape of at least one surface of the plural reflectionsurfaces is a free-form surface that does not have a rotational centralaxis.
 25. An image pickup device comprising a reflection optical deviceaccording to claim 1 and a detector for converting light intensity intoan electric signal.
 26. The image pickup device according to claim 25,wherein the detector is a two-dimensional image pickup element.
 27. Theimage pickup device according to claim 25, wherein the detector hassensitivity with respect to light beams in the infrared region.
 28. Amultiwavelength image pickup device comprising a reflection opticaldevice according to claim 1 and a detector having sensitivity withrespect to light beams in plural different wavelength bands.
 29. Themultiwavelength image pickup device according to claim 28, wherein thedetector has a light flux dividing member for dividing light fluxes intolight fluxes in different wavelength bands and detection surfacescorresponding to the plural divided wavelength bands.
 30. Amultiwavelength image pickup device comprising the reflection opticaldevice according to claim 1 and the detector having plural regions,which have sensitivity with respect to light beams in differentwavelength bands, in the same detecting plane.
 31. A vehicle-mountedmonitoring device, comprising the image pickup device according to claim25 and a display for conveying a picked-up picture image to a driver.32. A vehicle-mounted monitoring device, comprising the multiwavelengthimage pickup device according to claim 28 and a display for conveying apicked-up picture image to a driver.